Cats
Genetically Impossible Kittens and Gender Anomalies". This article only considers normal
tortoiseshell cats.
Jean Bungartz referred to tortoiseshell-and-white cats as "Spanish cats" in his 1896 book "Die
Hauskatze, ihre Rassen und Varietäten" (Housecats, Their Races and Varieties) in "
Illustriertes Katzenbuch" (An Illustrated Book of Cats) though he said it was hard to explain
why they got the name as they were not restricted to the Pyrenean peninsula.
HOW TORTOISESHELL PATTERNS OCCUR
The ginger colour of cats (known as "yellow", "orange" or "red" to cat breeders) is caused by
the "O" gene. The O gene changes black pigment into a reddish pigment. The O gene is
carried on the X chromosome. A normal male cat has XY genetic makeup; he only needs to
inherit one O gene for him to be a ginger cat. A normal female is XX genetic makeup. She
must inherit two O genes to be a ginger cat. If she inherits only one O gene, she will be
annaabi.ee 
